Nervous System: Electrochemical Impulses

Question 1

Nerve Impulses

Answer 1

• conducted along AXON
• one direction
• away from cell body
• movement of ions thru nerve cells membrane creates difference of charge
• Difference of charge btwn inside n outside of cell is called potential difference or membrane potential

Question 2

Resting potential

Answer 2

• voltage difference across nerve cell membrane at rest
• value is -70mV
• inside of cell negative relative to outside
• high concentration of K inside cell and higher concentration of NA outside
• neg charge bcs of SO4 n PO4
• called polarized membrane

Question 3

Action Potential

Answer 3

• Voltage difference across nerve cell membrane when nerve is excited
• aka: nerve impulses

Question 4

Steps of Depolarization

Answer 4

1. Neuron receive stimulus
2. Some Na channels open, Na go into cell (via facilitated diffusion)
3. K channels remain closed, K does not leave n is trapped inside neuron
4. Na and K in neuron > voltage in cell become more pos
5. Cl remain out > neg charge outside of cell
6. When threshold potential is reached (-50mV), action potential occurs and all Na channels open

Question 5

Define Threshold Potential

Answer 5

• membrane potential that neuron must reach to initiate action potential
• usually -50mV

Question 6

Action potential

Answer 6

• When threshold potential is reached, action potential is triggered
• The strength of each stimulus is the same, no matter the strength of the stimulus
• strong stimulus result in more frequent action potential, not stronger.

Question 7

Define Repolarization

Answer 7

• Re-establish og resting membrane

- Prepare neuron for next action potential.

Question 8

Steps of Repolarization

Answer 8

1. When potential reaches to -40mV, Na channels close
2. K channels slowly open to release K outside of cell (via facilitated diffusion)
3. Charge outside cell becomes neg again, restoring resting membrane.`

Question 9

Hyperpolarization

Answer 9

• Bcs K channels close slowly, more K is released out of the cell after repolarization
• Makes cell more negative (-85mV) than the resting membrane potential`

Question 10

Na/K pump

Answer 10

• Restores the resting membrane by transporting Na out of cell and K back into cell.
• Uses ATP to pump 3Na out and 2K inside cell

Question 11

Why does neuron need to restore to resting membrane potential?

Answer 11

Because a neuron is not able to trigger another action potential until it is at rest.

Question 12

Refractory Period

Answer 12

• time taken to restore resting membrane from the hyperpolarized state
• prohibits AP to travel backwards

Question 13

Transmission of Action potential

Answer 13

• action potential do not travel along axon, occurs at one point of axon
• depolarization of one point causes the next section to depolarize
• AP cannot travel backwards bcs of refractory period
• Direction goes from dendrite to axon

Question 14

Speed of action potential depends on:

Answer 14

• diameter of axon (bigger =faster)

- Myelin which causes saltatory conduction

Question 15

Define Saltatory Conduction

Answer 15

• Ion channels are concentrated in the node of ranvier
• Impulses jump from node to node skipping regions that are covered by Schwann Cells (myelin sheath)
• Depolarization only occurs where there is no myelin sheath